In the prior art, multi-function electronic watches are known that include a time base for calculating a value representative of a time-related item of information, namely the current time, a volatile time counter which stores the calculated value representative of the current time and the position of the analogue display means, namely the hands, operating in synchronism with this calculated value in a first operating mode, called the “time mode”, and operating in an asynchronous manner with the calculated value in a second “non-time-related” mode, like for example a chronograph mode, a compass mode or even a weather mode.
For obvious reasons of cost and available space in such multi-function watches, it is preferable to power the watch by means of a primary energy source. However, at the end of the life of such a primary energy source, on the one hand, the hands are stopped when the energy provided by the source is perceived to be insufficient to move them, and, on the other hand, the value of the counter is corrupted when the source is insufficient to power the time counter and zero reset when the primary energy source is replaced. Thus, after the primary energy source has been replaced, the value contained in the time counter no longer corresponds to the value corresponding to the position in which the hands were or have been stopped. In cases where the user resets the time after replacing the primary energy source, as the hands operate in synchronism with the time counter value, the shift between the position of the hands and the value contained in the time counter remains. Although this shift in no way prevents the watch from operating normally in its time mode, this raises a problem when the user wishes to use the non-time related mode of the watch. Indeed, in the non-time related mode, the watch is supposed to place the hands in a reference position which it determines as a function of the value contained in the time counter, which is supposed to match the actual position of the hands. Thus, the hands are brought into incorrect positions in the non-time related mode, which causes the user to think that the watch is defective which is evidently undesirable.
One example of this malfunction is detailed in relation to FIGS. 1a to 1h. In this example, each hand is moved by means of an independent motor.
FIG. 1a shows, in time mode, dial 2 of the watch on which hands 4 and 6 indicate the current time, namely 10 minutes past 10 o'clock, in synchronism with the value contained in the time counter 8 of the watch.
FIG. 1b shows the same watch five minutes later, in non-time related mode, the latter being activated by the user. In this non-time related mode, hands 4 and 6 indicate a predetermined reference value, i.e. here both hands point towards the first indicator corresponding to 1 o'clock or 5 minutes, an additional indicator 10 being able to be arranged opposite on the bezel (not shown), or even on the dial or the crystal. Thus, the user knows that he is in the non-time related mode corresponding to indicator 10, the hands pointing in that direction. The correct positioning of the hands can be achieved simply by moving the hands independently of each other by means of their respective motor, since the electronic circuits of the watch know the start position of the hands defined by the value in the time counter, both being synchronous and the end position of the hands, the latter being predetermined for the non-time related mode selected. During operation in the non-time related mode, the value of the counter continues to be incremented by the time base, with the hands no longer being in synchronism with said value.
In FIG. 1c, the watch has returned to time mode, either because the user has activated the time mode, or because the watch has automatically returned to the time mode after, for example, a timeout. The time indicated by hands 4 and 6 is now 20 minutes past 10 o'clock.
In FIG. 1d, the power supplied by the primary energy source of the watch has become insufficient to move hands 4 and 6, which, in the example shown, continue to indicate 20 minutes past 10 o'clock, whereas the value contained in the time counter may continue to be incremented, this updating of the counter value consuming less energy.
FIG. 1e shows either the state of the watch at the end of life of the energy source, or just after the energy source has been replaced. In the first case, the time counter is not longer being powered and the value that it contains is corrupted (reset to zero), the hands still indicating 20 minutes past 10 o'clock. The user is then aware that he has to change the energy source when he sees the hands have stopped, which brings us to the second case following the replacement of the energy source. In the second case, the counter value is reset to zero, or any other constant pre-set value, the powering of the counter having been interrupted for a relatively long time period, following replacement of the energy source. In the example shown, as the replacement has just occurred, the hands still indicate 20 minutes past 10 o'clock. It will thus be noted that there is a shift between the value contained in the time counter and the value corresponding to the real position of the hands.
Following the replacement of the energy source, as is shown in FIG. 1f, the user has reset the time of the watch, for example in a conventional manner by means of a time setting crown. It should be noted that in the time reset operating mode of the watch, when the hands are driven, the value contained in the counter can be altered in synchronism (8a) with the movement of the hands or remain unchanged (not shown). In the example shown, the current time is 15 hours and 30 minutes. The user must thus rotate the hands by 5 hours and 10 minutes to bring them into a position where the correctly indicate the current time. In the first case where the counter (8a) remains synchronised during time resetting, the value that it contains is then 5 hours 10 minutes. In the second case (not shown) where the counter is not synchronised with the hands when the time is reset, the value that it contains remains unchanged, namely 0 hours and 0 minutes. Thus in both cases, there is still a shift between the value contained in the counter and the value corresponding to the real position of the hands.
FIG. 1g shows the position of the hands on the dial in the case presented in FIG. 1f, i.e. when the value contained in the counter can be altered in synchronism, when the user again activates the non-time related mode. In the example shown, the user has activated the non-time related mode 5 minutes after having replaced the energy source. The value contained in the counter is thus, 5 hours and 15 minutes (counter 8a), when the value contained in the counter can be altered in synchronism. Figure h shows the same situation as FIG. 1g for the case when the value contained in the counter remains unchanged: the value of the counter 8b will then be 0 hours and 5 minutes.
In the first case (FIG. 1g), hour hand 4a is shifted by 4 hours and 15 minutes in the anti-clockwise direction. This value of 4 hours 15 minutes is obtained by taking the difference between the value contained in the counter 8a, namely in this example 5 hours 15 minutes, and the predetermined reference position of hour hand 4a in the non-time related mode, namely in this example 1 o'clock. In the knowledge that, in the example concerned, hour hand 4a is initially between the 3 and 4 o'clock indicators, the movement of 4 hours 15 minutes brings the latter to point between the indicators corresponding to 11 and 12 o'clock. The minute hand 6a is shifted 10 minutes in the anti-clockwise direction. This value of 10 minutes is obtained by taking the difference between the value corresponding to the minutes contained in counter 8a, namely 15 minutes in this example, and the predetermined reference position of minute hand 6a in the non-time related mode, namely 5 minutes in this example. In the knowledge that, in the example being considered, minute hand 6a is initially pointing to 35 minutes, the movement of 10 minutes brings the latter opposite the indicator corresponding to 25 minutes. It will thus be observed that the hands of the watch each indicate a “fantasy” value instead of indicating the desired reference position for informing the user that the time mode has been selected. The user can thus quite rightly think that his watch is not working properly.
In the second case (FIG. 1h), the same calculation rules are applied and because of the shift between the real position of hands 4b and 6b and the value that is supposed to correspond in counter 8b, a “fantasy” result is also obtained. Thus, again the hands are not pointing in the direction of the desired reference position when the non-time related mode is activated by the user, who might thus doubt that his watch is working properly in this mode.
In order to avoid this shift between the real position of the hands and the value representative of this position in a counter, certain solutions of the prior art provide for the use of a non-volatile memory for storing the position of the hands. Thus, even in the event of a prolonged interruption to the power supply, due for example to replacement of the watch battery, the value corresponding to the position of the hands is maintained and thus actually corresponds to the real position of the hands. However, this solution is not desirable for evident reasons of manufacturing costs, and available space in the printed circuit of the watch.